Various different high temperature engineering plastics exist that can be used to form different parts and articles. In many applications, those skilled in the art have been attempting to replace conventional metal parts with those made from high temperature polymers. Various high temperature polymers exist that are strong, have excellent chemical resistance, have high rigidity, and are stable at high temperatures. Various advantages and benefits may be obtained if the above polymers can successfully replace metal parts in various embodiments. For example, the plastic parts are lighter, produce less noise, and are more resistant to chemical attack than many metals.
Although low temperature polymers may be molded into many different shapes, problems have been experienced in molding high temperature polymers into complex shapes. For example, problems have been experienced in manipulating high temperature polymers during various molding processes, including during extrusion blow molding.
For instance, when blow molding hollow articles having a complex shape, problems have been experienced in controlling and/or obtaining uniform wall thickness during formation of a parison and in manipulating the parison into a particular shape once the parison is formed. During complex blow molding operations, tubular members are formed that are constantly undergoing shape changes. In one application, for example, a parison is extruded in a downward direction while the polymer composition remains at an elevated temperature. The polymer composition is extruded through an annular opening or die until a desired length of the parison is obtained. The parison should maintain uniform wall thickness while it is being extruded and resist stretching or elongation under only its own weight until a desired length is obtained to begin blow molding. The parison may also be maneuvered for example by a robot during extrusion to change the angular displacement of the tubular form to a specific shape.
The mold closes onto the tubular form once the desired length is attained and a needle is inserted at one end of the closed parison to allow a gas or air to be injected into the tubular form to blow mold the article into its final shape. During the above process, past compositions had a tendency to sag during the process causing changes to the thickness of the parison inadvertently. Sagging is a low shear phenomenon and is affected by the melt strength or melt elasticity of the polymer composition.
Tubular articles capable of functioning in high temperature environments are particularly needed in some industries, such as the automotive industry. For example, car engines and truck engines include various ducts, tubes and exhaust passageways that are designed to convey fluids, such as gases and liquids, to and from the engine. In some embodiments, hot exhaust gases are fed through the above ducts or tubes. In other embodiments, the ducts or tubes may convey lower temperature fluids but are placed in close proximity to engine locations that operate at high temperatures. As engine compartments are becoming more compressed, the above ducts and tubes have had to assume complex three-dimensional shapes in order to fit around the engine and the other parts of the vehicle. In the past, such ducts and tubes have been conventionally made from metals. The present disclosure, however, is directed to engine conduits as described above and other tubular members that are made from high temperature polymers. More particularly, the present disclosure is directed to improved high temperature articles and particularly to tubular members made from high temperature polymers that have a relatively complex shape.